Automobile body panels are typically made by shaping low carbon steel or aluminum alloy sheet stock into desired panel shapes. Sheet panels may be made using conventional stamping technology or utilizing alternative methods such as Super-plastic forming (SPF) processes and Quick-plastic forming (QPF) processes. The above-referenced plastic forming processes have the advantage of creating complex shaped parts from a single sheet of material. Such plastic forming processes eliminate the need for joining several panels formed in a stamping process to create an overall panel assembly.
Super-plastic forming processes generally utilize a metal alloy, for example, aluminum and titanium alloys that have high ductility when deformed under controlled conditions. Such metal alloys are capable of extensive deformation under relatively low shaping forces. Super-plastic alloys are characterized by having tensile ductility in the range of from 200% to 1,000% elongation.
Super-plastic forming processes, such as that disclosed in U.S. Pat. No. 5,974,847 discloses a process in which an aluminum alloy 5083 sheet is heated to a desired SPF temperature of about 500° centigrade and then subjected to a stretch forming operation. The stretch forming operation includes placing the heated aluminum sheet in a tool that has upper and lower dies. The dies engage along the edges of the sheet and then high-pressure gas is introduced against the backside of the metal sheet through a suitable gas passage, stretching the metal sheet into compliance with the forming surfaces of the die. While the Super-plastic forming process allows for the creation of complex shaped parts, the process utilizes cycle times that may be too long for high volume manufacturing situations. The Super-plastic forming process also utilizes complex and expensive tooling that occupies a significant amount of space in a manufacturing facility.
Similarly, U.S. Pat. No. 6,253,588 discloses a Quick-plastic forming process in which large aluminum 5083 alloy sheets are formed into complex shaped parts at much higher production rates than those achieved by the SPF processes. The aluminum alloy sheets are heated to a forming temperature in the range of from 400° C. to 510° C. and are stretch formed against a forming tool utilizing high pressure gas against the back surface of the sheet. The fluid pressure is preferably increased continuously or stepwise from 0 psi to a final pressure of from 250 to 500 psi.
Complex parts produced utilizing the Quick-plastic forming process often use tooling that includes a binder that has a significant curvature to create the shape of the panel to be produced. With such curved binders, there is often a limited press opening that diminishes loading and accurately locating a flat blank sheet. To assist the forming operation and enable repeatable location of the blanks, the blank must often be bent to match the curvature of the binder. Current Quick-plastic forming processes utilize separate tooling inside a hot forming press for bending the blank to match the binder curvature. Such tooling occupies a significant amount of a manufacturing facility which could be utilized for additional forming tooling if the aluminum sheet could be bent to conform to the shape of the tool's binder.
There is, therefore, a need in the art to further optimize a Quick-plastic forming or Super-plastic forming process by eliminating tooling inside a hot forming press for pre-bending the blank to match the binder curvature. Such a process and an apparatus for carrying out the bending would realize significant cost savings when utilizing a Super-plastic forming or Quick-plastic forming operation.